1. Field of the Invention
The present invention generally relates to a communication system, and in particular, to a ranging apparatus and method of a mobile station in a communication system with a relay station, and a system thereof.
2. Description of the Related Art
Generally, in a communication system, a mobile station performs a ranging procedure for synchronization information acquisition, power calibration, bandwidth allocation request, and the like. Types of the ranging are classified into initial ranging, maintenance ranging (also known as ‘periodic ranging’), and bandwidth request ranging.
A description will now be made of conventional ranging.
Initial ranging is performed to set a correct timing offset between a mobile station and a base station, and to calibrate transmission power.
Periodic ranging is periodically performed by the mobile station to adjust its channel condition with the base station.
The bandwidth request ranging is performed by the mobile station to make a request for bandwidth allocation to perform actual communication with the base station.
FIG. 1 shows initial ranging between a base station and a mobile station in a conventional communication system.
In FIG. 1, a Base Station (BS) 100 receives a ranging sequence #1 102 and a ranging sequence #2 104 from a Mobile Station (MS) 120 and an MS 140, respectively. The BS 100 receives the ranging sequence #1 102 and the ranging sequence #2 104 at different times. Therefore, the BS 100 estimates a delay for timing offset calibration of ranging sequences from each of the MSs 120 and 140, and sends control messages 106 and 108 to the MSs 120 and 140 based on the estimated delay, respectively. The control messages 120 and 140 are provided to control the MSs 120 and 140 to transmit a signal in advance of or behind a unit time. Therefore, upon receipt of the control messages 106 and 108, the MSs 120 and 140 each transmit a signal to the BS 100 at a time in advance of or behind a particular time.
Communication systems are currently evolving from 3rd generation mobile communication systems into 4th generation mobile communication systems. Research on a 4th generation mobile communication system is being conducted for an increase in system capacity and extension of radio coverage, or cell coverage. A multi-hop scheme has been proposed for increasing system capacity increase and extending cell coverage. When a channel condition between a BS and a MS is poor, the proposed multi-hop scheme can install a relay station between the BS and the MS to form a multi-hop relay path via the relay station. In this manner, the MS can receive a wireless channel having a good channel condition. In addition, as the multi-hop scheme allows the MS located inside or outside the cell boundary where the channel condition is poor to use the multi-hop relay scheme, the MS can receive a higher-rate data channel and contribute to extension of the cell coverage of the system.
As described above, communication systems are evolving into systems employing a relay station for increasing system capacity and extending cell coverage. However, current conventional ranging procedures are for communication systems with no relay station and, currently, there is no ranging procedure for a communication system with a relay station. Therefore, a need exists for a ranging apparatus and method of a mobile station in a communication system with a relay station, and a system thereof.